(Economist) Wind-powered ships are making a comeback

AN OIL tanker that ferries nearly 110,000 tonnes of the black stuff between the Middle East and Europe does not sound like a green ship. But Maersk Pelican is unique among the world’s biggest cargo ships in that it does not rely on fossil fuels alone for propulsion. On September 29th it arrived in Saudi Arabia on its first voyage since the installation of two 30-metre rotor sails.

Coal- and oil-powered cargo ships wiped out wind power in the 19th century. But interest in wind propulsion, and in rotor sails in particular, is growing as shipping lines seek ways to slash fuel bills. Placed on a ship’s decks, these giant rotating cylinders propel it using the “Magnus effect”, the force that causes a spinning ball to curve through the air.

The concept was demonstrated by Anton Flettner, a German engineer, in the 1920s, but rotor sails failed to catch on, partly because coal was a cheap alternative. The first ones he made were metal and so heavy that they slowed ships.

The rotor sails that Norsepower, a Finnish firm, has developed are made of carbon fibre and are far lighter, says Tuomas Riski, its chief executive. They are also automated, so no extra sailors are needed to operate them, unlike Flettner’s version. As well as Maersk Pelican, Norsepower has already fitted them to several other ships, including Estraden, a ferry which operates between the Netherlands and Britain, and Viking Grace, which sails between Sweden and Finland.

The interest in the sails comes because they can slash fuel bills and emissions, says Tommy Thomassen, chief technical officer of Maersk Tankers. The Maersk Pelican’s two rotor sails will cut its fuel bills by 7-10%, he forecasts; if it added two more that could rise to 15-20%. Such savings help with another priority for the shipping industry; complying with new climate-change targets. In April the International Maritime Organisation, a UN agency, agreed to cut by half the global shipping sector’s carbon emissions from 2008 levels by 2050.

Sails can make serious contributions to that target. Most other technologies (such as adding bulbous bows) shave only a few percent off fuel bills. Electric batteries cannot store enough energy for long sea voyages.

Upfront costs remain a problem. Norsepower’s rotor sails cost €1m-2m ($1.15m-2.3m) to install; it takes five years on average to earn that back in lower fuel bills. Mr Riski hopes to slash that figure to three years by making the sails more cheaply in China. It would then become worthwhile for charterers, which only tend to lease ships for under three years, to install them.

Rotor sails are not the only ones about. Modern versions of the sort of sails fitted to conventional ships, as well as kites attached to the front of the vessel, have also been mooted as energy-saving solutions. But these are a health-and-safety risk to sailors in bad weather. Wind power may be back in fashion but no one needs to mount the rigging.